The goal of this protocol is to explore changes to microbial communities during the course of hospital care, and to determine the extent to which these alterations affect whether hospitalized patients become colonized with healthcare-associated organisms. The study enables collection of clinical specimens and associated medical data to evaluate the natural history, epidemiology, and genomics of patients who might become colonized or infected with a multi-drug resistant organism. Biological specimens including stool, sputum, and swabs will be taken from Clinical Center inpatients at least 2 years of age as frequently as daily through discharge, and at follow-up visits for up to 2 years from the date of enrollment. To understand possible pathogen colonization and infection of hospitalized patients, this protocol will assess the full complement of the microbial-host-environmental contributions including: (1) microbial genome and community; (2) patient s genotype, underlying medical condition, medical treatment; and (3) hospital practices and environment.